1. Technical Field
The technical field relates to touch panels mainly used to operate various electronic apparatuses.
2. Background Art
Many electronic apparatuses such as mobile phones and electronic cameras have been equipped with a light-transmitting touch panel on the top surface of a liquid crystal display with their increased functionality and diversity in recent years. Such an apparatus allows the user to switch between various functions by touching the panel with a finger, pen, or other pointing device while watching the screen of the liquid crystal display through the panel.
A conventional touch panel will now be described with reference to FIG. 4. In FIG. 4, which is a sectional view of the conventional touch panel, the dimensions of some parts are enlarged for easy understandings.
Touch panel 10 includes upper substrate 1, upper conductive layer 2, lower substrate 3, lower conductive layer 4, a pair of upper electrodes 5, a pair of lower electrodes 6, dot spacers 7, and frame-shaped spacer 8. Of these components, upper substrate 1, upper conductive layer 2, lower substrate 3, lower conductive layer 4, and dot spacers 7 are light-permeable. Rectangular upper conductive layer 2 is disposed on the bottom surface of upper substrate 1. Rectangular lower conductive layer 4 is disposed on the top surface of lower substrate 3.
Upper electrodes 5, which are made, for example, of silver paste are disposed along the left and right edges of upper conductive layer 2 and lower electrodes 6 are disposed along the front and rear edges of lower conductive layer 4 in FIG. 4. One end of each of upper electrodes 5 is extended to the front of the outer periphery of upper substrate 1, and one end of each of lower electrodes 6 is extended to the front of the outer periphery of lower substrate 3. Dot spacers 7 are disposed on the top surface of lower conductive layer 4, whereas spacer 8 is disposed along the inside of the outer periphery between upper substrate 1 and lower substrate 3. Dot spacers 7, which are made of an insulating resin, are shaped like hemispherical domes and arranged at intervals of 2.5 mm or less.
Upper substrate 1 and lower substrate 3 are bonded together at their outer peripheries via an adhesive (not shown) applied to one or both of the top and bottom surfaces of spacer 8. Thus, upper conductive layer 2 and lower conductive layer 4 are opposed to each other with a predetermined space therebetween.
Upper substrate 1 includes substrate layer 11, hard coat layer 12 disposed on the top surface of substrate layer 11, and light diffusing layer 13 disposed on the bottom surface of substrate layer 11. Substrate layer 11 is made, for example, of polyethylene terephthalate. Hard coat layer 12 is made of a synthetic resin such as an acrylic resin mixed with a fluorine-based resin. The top surface of hard coat layer 12 is made lipophilic so as not to leave fingerprints when the user touches it. As a result, hard coat layer 12 has a surface tension of 30 N/mm or less. Light diffusing layer 13 contains an acrylic base, and silicon dioxide filler dispersed in the base. This filler functions to form asperities on the bottom surface of light diffusing layer 13.
Touch panel 10 thus structured is mounted on liquid crystal display 15 and installed on an electronic apparatus. Upper electrodes 5 and lower electrodes 6 are electrically connected to a control circuit (not shown) such as a microcomputer included in the apparatus.
When the user presses the top surface of upper substrate 1 with a finger or pen according to the display on liquid crystal display 15, upper substrate 1 is bent. Under the touched area of upper substrate 1, upper conductive layer 2 comes into contact with lower conductive layer 4. Then, the control circuit sequentially applies voltages to upper electrodes 5 and lower electrodes 6, thereby detecting the touched area from the voltage ratio between these electrodes. This enables switching between various functions of the apparatus.